Percussion tone electrical musical instrument



' Sept. 20, 19 J. M. HANERT PERCUSSION TONE! ELECTRICAL MUSICALINSTRUMENT 2 Sheets-Sheet 1 Filed Jan. 13, 1954 Sept. 20, 1960 FiledJan. 13. 1954 J. M. HANERT PERCUSSION TONE ELECTRICAL MUSICAL INSTRUMENT2 Sheets-Sheet 2 United States Patent PERCUSSION TONE ELECTRICAL MUSICALINSTRUNIENT John M. Hanert, Des Plaines, Ill., assignor to Hammond OrganCompany, Chicago, Ill., a corporation of Delaware Filed Jan. 13, 1954,Ser. No. 403,673

8 Claims. (Cl. 84-126) My invention relates to electrical musicalinstruments and more particularly to means for producing tones havingpercussive decay envelopes.

A highly desirable musical effect is that of producing percussive toneseither with or Without sustained accompanying tones. The chime orbell-like tones embellish and enhance the customary organ tones and mayvery advantageously be employed for emphasis and contrast.

By the use of the present invention, percussive tones may be obtainedfrom any electric or electronic organ, or a similar instrument, by theaddition of a relatively small number of parts at slight additionalcost. The primary object of the invention is, therefore, to provide animproved electric organ whereby tones with percussive intensityenvelopes may be produced.

A further object is to provide percussive envelope tone controllingmeans which may be used at will and which does not in any way affectnormal playing of the instrument.

A further object is to provide an electronic instrument having twomanuals, or a divided manual, in which means are provided so that toneswith percussive decay envelopes may be played with one hand whilesustained tones having a vibrato may be played with the other hand.

A further object is to provide an electric organ capable of producingmusical effects similar to those produced by chimes, bells, xylophones,marimbas, harps and other percussion type instruments fromnon-percussive sustained tone generators, the tone intensity envelopeshaving very sharp attack and controllable decay.

Other objects will appear from the following description reference beinghad to the accompanying drawing in which:

Fig. l is a schematic wiring and block diagram of an instrumentembodying the invention;

Fig. 2 is a schematic wiring diagram of a modified form of theinvention; and

Fig. 3 is a schematic wiring diagram of a further modification of theinstrument.

The instrument shown in Fig. 1 comprises a plurality of electric tonesignal generators having one terminal connected to ground and theirother terminals connected through non-robbing resistors R12 to switches14 operated by playing keys 16 of the upper manual and keys 17 of thelower manual. The switches 14 of the upper manual make contact withcollecting bus bars 20 to 28 which respectively collect signals of thepitch corresponding to the sub-fundamental, the sub-third, fundamental,and the second, third, fourth, fifth, sixth, and eighth harmonics of thefundamental. Similarly, switches of the lower manual make contact withbus bars 29.

Reference may be had to the patent to Laurens Hammond No. 1,956,350, formore complete disclosure of the generators 10, the key operated switches14, and associated parts and circuits, these being new well-known in theart. It is to be understood, however, that the invention may be appliedto other kinds of electrical musical instruments, as will appear morefully hereinafter.

Patented Sept. 20, 1960 The only essential respect in which the keyoperated switches for use in the present invention differ from the keyswitch mechanism shown in said prior patent is that the actuators forthe switches 14 are constructed in such manner that the switches 14 forthe second and third harmonics, namely the switches 14 which makecontact with bus bars 23 and 24, will close prior to the closing of theremaining switches 14 upon depression of the key, and, upon the releaseof the key, these two switches should be the last to open. Suchsequential operation of the eswitches 14 is desirable but not essential.If the switch structure were made such that upon release of the key theswitches 14 open at exactly (within about 25 milliseconds) the sameinstant, there will be no opportunity for an audible spurious tone to besounded upon the release of the key.

Each of the bus bars 20 to 28 of the upper manual, and bus bars 29 ofthe lower manual, is suitably connected to an amplitude regulatingdrawbar 30 which is adapted selectively to make contact with any one ofa plurality of cont-act strips 32, as more fully disclosed in the patentto H. E. Meinema No. 2,565,512. The uppermost contact strip 32 isconnected to ground and the lowermost contact strip is connected to oneterminal of the primary winding 34 of an output transformer 36, theother terminal of which is connected to ground. The other contact stripsare connected to graduated taps on a resistor R38. Thus, the variouspartials of the tones may be controlled as to intensity by selectivelysetting the drawbars 30. The secondary of the transformer 36 isconnected to an amplifier 40 which in turn is connected to a vibratoapparatus 42, the output of the latter being amplified by a poweramplifier and volume control 44 and supplied to a speaker 46.

In addition to its usual controls, the instrument is provided with apercussion on and off tablet 50, a second or third harmonic tablet 52,and a slow or fast decay tablet 54. The tablet 50 is connected tooperate switch fingers 55, 56, 57, and 58 while the tablet 52 similarlyoperates switch fingers 60, 61, 62, and 63. When the control tablet 50is in its upper position, switch finger 55 connects conductors 64 and66, thus maintaining the third harmonic collecting bus bar 24 connectedto its drawbar 30. Similarly, switch finger 56 connects couduetors 68and 69 so that the bus bar 23 for collecting the second harmonic isconnected to its drawbar with the result that the drawbars will separatein the normal manner. Likewise, switch finger 57 connects conductors 70and 71 thereby connecting the eighth harmonic collecting bus bar 28 toits drawbar 30. Thus, when the tablet 50 is in the off position theinstrument may be played in the usual manner with the usual results.

When the tablet 50 is in its lower or on position the third harmonic busbar 24 is connected through conductor 64 and switch 60 to the primarywinding 74 of a matching transformer 76. The secondary winding 78 ofthis transformer has one terminal connected to ground and to oneterminal of the primary winding 74. The other end of the secondary 78 isconnected to the control grid 80 of amplifying triode 82. A certainamount of negative feedback from plate to grid is provided through acapacitor C84 and a resistor R86 connected in series between theseelectrodes. The cathode 88 is connected to ground through a self-biasresistor R90 shunted by a bypass capacitor C92. Plate current issupplied through the primary 94 of a coupling transformer 96 from asuitable terminal of the power supply, indicated as a terminal +260 v.The secondary 98 of the transformer 96 has its terminals respectivelyconnected to grids 100 and 101 to triodes :102 and 103, such connectionbeing effected through resistors R104 and R105 respectively. Theseresistors form part of a key click filtering mesh,

which also includes a capacitor C106 and a resistor R107 connectedbetween the grids 100 and 101.

The cathodes of the triodes 102 and 103 are connected to a +36 v.terminal and are connected to a center tap of secondary winding 98through a decay determining capacitor C109. The plates of these triodesare connected to the terminals of the primary winding 108 of atransformer 110, the center tap of the primary "108 being connected to asuitable terminal of the power supply, indicated as +200 v. Thesecondary 1:12 of transformer 110 has one terminal grounded and itsother terminal connected by a conductor 114 to a percussion volumeadjusting means, comprising an adjustable resistor R116 and a fixedresistor R118 which are connected in series between the conductor 114and ground. These resistors are shunted by a switch finger 58 when thetablet. 50 is in its upper position so that the second ary winding 112is short circuited and no noise or extraneous signal can appear acrossthe secondary 1.12.

The ungrounded terminal of the secondary winding 112 is connected by acapacitor @120 and a conductor 122 to the input of the power amplifier44.

A tertiary winding 126 on the transformer 96 has one terminal connectedto ground and its other terminal connected by a resistance R123 with theswitch finger 63. It will be noted that switch finger 63 may connectwith either conductor 130 or a conductor 132, that switch finger 62 mayconnect conductor 64 to conductor 130, that switch finger 61 may connectconductor 132 with a conductor 134, and that switch finger 60 mayconnect the primary winding 74 either to conductor 64 or to conductor134.

When the tablet 50 is in its on position and the tablet 52 is in theposition shown, the third harmonic of the tones corresponding to anyplaying keys 16 which may be depressed will be impressed across theprimary 74, will be amplified by the triode 8 2, and transmitted throughthe transformer 96 to the output as previously described. However, thesesignals also appear across the tertiary winding 126 and are transmittedthrough resistor R128, switch 53, conductor 130, switch 55, andconductor 66 to the drawbar 30 for the third harmonic. The number ofturns on the tertiary winding is such that the amplitude of the signalon the third harmonic drawbar 30 will be the same as that of the signalappearing on the third harmonic bus bar 24. Thus, the third harmonictones will have their intensity determined by the position of adjustmentof the drawbar 30 for the third harmonic.

The triodes 102 and .103 are normally in condition to conduct the signalby virtue of the fact that a center tap on secondary winding 98 isconnected by a conductor 140 to the cathode 141 of a triode 142operating as a diode. The plate 143 of this triode is connected to a +32v. terminal through resistors R144 and R145, the junction between theseresistors being capable of being connected to ground through a resistorR146 upon closure of a switch .148 operated by the decay rate controltablet 54. The conductor 140 is connected through a relatively highvalue decay rate determining resistor R150 which is connected to thecontactor of a potentiometer R152, the terminals of latter beingrespectively connected to ground and a +32 v. terminal of the powersupply. When fast decay is desired the tablet 54 is operated to closethe switch 160 and to open switch 148. Closure of switch 160 connects aresistor R162 in parallel with R150, the resistance of R162 being but afraction of the resistance of R150. Both the plate 143 and the grid 164of triode 142 are connected by a low value resistor R166 to a conductor168, which, when the key 50 is in its on position, is connected byswitch 57 with the eighth harmonic bus bar 28 through conductor 70.

' The potentiometer R152 is adjusted to a position such thatwhen thetriode 142 is not conducting a, bias voltage approximately sufficient tocutoff triodes 102, 103 may be impressed upon their grids 100, 101.

When the tablet 50 is in its upper position the instrument is capable ofplaying sustained tones in the usual manner because switches 55, 56, and57 connect the third, second, and eighth harmonic collector bus bars 24,23, and 28 to their associated drawbars 30, and the secondary 112 of theoutput transformer is effectively shunted because switch 50 is closed.

Whenever the percussion effect is desired the tablet 50; is depressed,whereupon the third harmonics of the notes corresponding to playing keys16 which are depressed will, as previously described, be impressedacross the primary 74 of the transformer 76. These signals are amplifiedand transmitted in push pull through the triodes 102, 103 and thussupplied to the amplifier 44 and speaker 46. However, depression of aplaying key, such as key 16, will cause the bus bar 20 to be connectedto ground through one or more. generators 10 and resistors R12. Thesegenerators have low impedance and the values of the resistors R12 arelow with respect to the values of resistors R144 and R so that the plate143 and grid 164 have their potential rapidly lowered to a valuesufficient to prevent current flow through the triode 142.

As a result, the potential on conductor 140, and hence on the grids ofthe triodes 102, 103 wfll begin dropping to the cutoff value determinedby the setting of potentiometer R152. The rate at which the bias ontriodes 102 and 103 increases is determined mainly by the values ofcapacitor 0109 and resistor R150, and also by resistor R162 when thelatter is connected in the circuit.

The tone produced will thus commence substantially instantaneously andwill decay gradually, or quite rapidly, depending upon the position ofthe decay control tablet 54. This extremely rapid attack is highlydesirable in simulating the tones of the percussion family ofinstruments but would be difficult to produce, in a practical sense, bythe use of control tubes Whose transmission might be controlled byexternal excitation in a manner similar to that in which the slow decayportion of the envelope is obtained in the instrument herein disclosed.An extremely high degree of balance in the control tubes and associatedcomponents would be required, which is practically impossible to obtainwith ordinary vacuum tubes. The requirement for good balance isespecially apparent when one considers that the control tubes must bevirtually free from distortion in order that chords may be playedwithout objectionable intermodulation. This means that only a smallportion of the grid voltage plate current characteristic could beutilized, which would make it necessary that the steady component of theplate current be large in comparison with the alternating components,thus increasing the probability of producing a thump, due to theunbalance of the two steady plate current components in the controlstubes.

In the instrument disclosed herein the envelope control apparatusoperates in a manner normally to provide full gain, thus substantiallyinstantaneously transmitting the attack portion of the envelope uponclosure of the playing key operated switches 14. The decay portion ofthe envelope is relatively slow and therefore substantially free ofundesirable transients in the audio range. Likewise, the change in gainof the envelope control apparatus which occurs when the playing keys arereleased may also be relatively slow, being limited only by the intervalbetween the release of one key and the depression of the next key as themusician plays in the required non-legato manner. Thus, this apparatusexercises little control on attack but is effective to cause slow decaywithout the necessity of having perfect balance in the envelope controlapparatus. From a practical standpoint, this novel feature is of greatimportance.

It will be noted that when the table 54 is set for fast decay, resistorR146 is removed from the circuit so that the potential on the plate 143and grid 164 will be higher and the tones will sound initially at a highintensity due to the reduced grid bias on triodes 100 and 101. Ofcourse, the tones will then decay much more rapidly because therelatively low value resistor R162 is in parallel with resistor R150.The values of the components are such that the total energy of thepercussive tone with fast decay will be about the same as that of thetone with slow decay.

When it is desired to use the second harmonics of the tones fordetermining the pitch of the percussion tones, that is, whether thepitch of the percussion tone is but one octave higher than the nominalpitch of the playing keys 16 which are depressed instead ofcorresponding to the third harmonic of the nominal pitch of the playingkeys, the tablet 52 is depressed. Under these conditions the signalstaken from the second harmonic collecting bus bar 23 are transmittedthrough conductors 68, 134 and switch 60 to the primary winding 74. Thesignals impressed upon the third harmonic bus bar 24 are transmittedthrough conductor 64, switch 62, conductor 130, switch 55, and conductor66 to the third harmonic drawbar 30. Thus, the third harmonic sustainedtones will be transmitted to the output system of the instrument in theusual manner and will not sound percussively.

The invention is of particular usefulness when, as disclosed herein, itforms part of a two manual organ of the type which has a phase-shiftingvibrato apparatus, of the type shown in my prior Patent No. 2,382,413.Such instrument, provided with the improvement of this invention, may beplayed to produce orchestral percussion eifects without vibrato byplaying on one manual while providing sustained accompaniment tones withvibrato by playing on the other manual. Furthermore, the manual which isused to control the supply of percussion signals may also be employedsimultaneously to control the supply of sustained tones with vibrato, tofurther enhance the musical efiects. Similar musical results may beobtained with a single split, or divided, manual in which case only thetreble notes would be played with percussive decay.

The instrument is unique in that from a single signal generator capableof producing a sustained tone, a percussive decay tone devoid of vibratomay be derived by playing on one manual, while at the same time asustained tone with or without vibrato may be derived from the samegenerator by playing on either manual, or in fact by playing the samekey which controls the production of the percussive tone.

The contrast of percussive tones devoid of vibrato played on one manualwith sustained tones with vibrato played on the other manual ismusically interesting and pleasing.

When playing percussive chords on the instrument with the tablet 54 setfor fast decay, it is desirable that some care be exercised indepressing the keys simultaneously so that each element of the chordwill be sounded with the same initial intensity. When the percussioneifect is being used and the playing keys are depressed, the listenerfirst hears the tone at maximum intensity followed by a slow or rapiddecay, depending upon the setting of tablet 54. After this the tone maybe made to continue to sound as long as the keys are held depressed, ifthe drawbar 30, corresponding to that of the harmonic used forpercussion eifect, is not connected to the grounded strip 32.

When the intensities of the vibrato modulated tone signal supplied bythe vibrato apparatus 42 is comparable to that of the non-vibratorsignal supplied through the percussive output channel, a very pleasingpercussive vibrator chorus is produced in which the initial portion ofthe intensity envelope sounds with both vibrato and non-vibratocomponents of the same pitch. At the percussive tone subsides, thecharacter of the tone smoothly changes to that of the pure vibrator tonewhich is supplied by vibrator apparatus. This variation in chorus efiectis a pleasingly attractive and unusually different type of percussivetonal envelope. In general, the effect is similar to that of a largechorus of percussive instruments.

In playing musical selections it will frequently be desirable tointersperse percussion and sustained tones. The player may accomplishthis with facility by playing in a legato manner for producing sustainedtones and in a detached manner for producing percussive tones. That is,for playing sustained tones, the last key depressed is held down untilthe next key is depressed, but when a percussive tone intensity envelopeis desired the last key depressed is released before the next key isdepressed.

While the values of most of the components are not critical, it has beenfound that excellent musical results are obtained if their values are asset forth below. Wide variations in these values are possible withoutdetracting appreciably from the quality of the music which may beproduced.

R12 ohms R86 megohms R104 kilohms R105 d0 R107 do R116 do R118 do R128ohms R144 kilohms R145 do R146 megohms R150 do.. R152 kilohms R162megohm 1 R166 kilohms 5 C84 microfarads .05 C106 do .01 C109 do.. .3C120 do .00015 Triode 82 6C4 Triodes 102 and 103 12AU7 Triode 142 6C4The invention may be embodied in various forms and may be used withinstruments in which complex musical tones are generated. Such tones aregenerated and transmitted to the output system under the control of theplaying keys. Figs. 2 and 3 illustrate two modifications of theinvention in which the initial reception of a tone signal at the inputof the output system results in producing the percussion effect. Indescribing these figures, corresponding reference characters will be applied to parts corresponding to parts shown in Fig. 1.

Referring to Fig. 2, a generator 170 is adapted to have its outputconnected to the control grid of an amplifying triode 82 upon closure ofa playing key operated switch 174, the switch connecting the generator170 to the control grid of triode 82 through a decoupling resistor R176.The generator 170 is intended to be representative of an oscillator,vibrating reed generator, or other generator of electrical musical tonesignals. In this embodiment the tertiary winding 126 of transformer 96has one terminal connected to the cathode of rectifying triode 178, theother terminal of this Winding being connected by a conductor to a +32v. terminal of the power supply. The plate of triode 178 is connected tothe control grid 164 of triode 142 through a pair of series resistorsR182 and R183 which, together with shunt capacitors C184, form a filterfor removing the audio frequency components which are present along withthe desired direct current component in the output of the rectifier 178.When a tone signal appears in the winding 126, a filtered DC. voltage,negative with respect to the potential of +32 v. on conductor 180, willappear on the grid 164. This negative voltage appearing on the grid andplate of triode 142, which is operating as a diode, lowers the potentialon these electrodes sufficiently with respect to the po tentials on, thecathode so as to render this tube nonconducting, thereby permitting thepotential on capacitor C109 gradually to drop to the potentialdetermined by the setting of the potentiometer R152, in the mannerpreviously described with respect to the form of the invention shown inFig. 1. 7

It will be apparent that whenever the playing key operated switch 174 isclosed, the appearance of the signal in the tertiary winding 126 willrapidly result in rendering tube 142 non-conducting with theaforementioned result of producing a tone having a percussive decaycharacteristic.

In the form of the invention shown in Fig. 3 the signal is, as in thecircuit shown in Fig. 2, utilized to control the commencement of thepercussion decay portion of the tone intensity envelope. The signalappearing on the plate of triode 82 is transmitted through a conductor190, a capacitor C192, and a resistor R194, to the grid of a triode 196which forms the first of a cascaded series of three amplifying and waveclipping stages, the second and third of which include tn'odes 197 and198.

The output of the third stage, which includes the triode 198, isimpressed upon the control grid 200 of an amplifying triode 202 whoseplate current is normally cut off by virtue of the fact that the controlgrid is connected to a -35 v. terminal of the power supply throughseries resistors R204 and R266. The plate of triode 202 is connected toa +260 v. terminal through the coil 2&8 of relay 210. A capacitor C212is connected in parallel with the relay coil 208 to prevent chatteringin the event that the audio frequency input is in the low bass range.The normally closed contacto-r 214 of the relay connects conductor 140through resistors R144 and R145 to a +32 v. terminal so that the triodes103 and 194 are normally conducting.

The relay contactor 214 thus operates in the same manner as the triode142 of Fig. l in that it operates to cause the tone to start decay theinstant it commences. The effect of the amplifying and clipping stages,which include triodes 1%, 197, and 198, is to minimize relay chatter inthe event that two closely related frequencies are transmittedsimultaneously. When two such frequencies are simultaneously present theresulting wave form will contain periods of instantaneous low amplitudeenergy which would cause corresponding periods of conduction in theoutput triode 2%. The duration of these periods of low instantaneousenergy is greatly minimized by the clipping action, which changes theWave of the super-position of the two input frequencies into one inwhich the amplitude of the wave is constant and in which rapidalternations occur at all times. The relatively small capacitor C212across the relay coil is effective to maintain the relay energy duringthe very short intervals of time at which the instantaneous energy is ata low value. Thus, the relay remains in operated condition withoutchattering whenever one or more playing keys are operated to cause audiotone signals to be impressed upon the conductor 190.

Upon depression of the playing key operated switch 174 the bias on thetriodes 103, 104 will therefore commence decaying as the capacitor C109discharges through the resistors R160 and potentiometer R152 in the samemanner as previously described to the effect in the circuit in Fig. 1.

In the embodiments of the invention shown in Figs. 2 and 3, the switch174 is intended to be representative of any means for controlling thetransmission of an electrical tone signal to the remaining parts of theapparatus shown. It might be in the form of a valve to cause vibrationof a reed with an electrostatic or electromagnetic pickup permanentlyconnected to the resistor R176 or itv mightv be in the form of a switchfor applying an exciting potential to one of a largev variety ofelectrical tone signal generators.

Similarly, the apparatus as shown in Figs. 2 and 3, might be utilized tomodify the tonal envelope produced by any mechanical musical instrumentthe tonal output of which would be picked up by a microphone, suitablyamplified, and supplied to the terminal of resistor R176. For example,the tone of an organ pipe could be made to sound percussively like thatof a piano and the tone of a piano could be made to decay away veryrapidly like that of a marirnba by using the percussive apparatus ofthis invention. Another novel application of this apparatus would be toprovide percussion envelopes added to the sustained tones provided by asingers voice, by the use of a microphone having one of its outputterminals connected to resistor R176.

The rectifier circuit and the means by which the potential on the gridsof the control tubes is determined is not claimed herein per se, but isclaimed in my Patent No. 2,828,659 granted April 1, 1958, on applicationSerial No. 442,523, filed July 12, 1954. The essence of the inventionclaimed herein resides in exercising a greater degree of amplitudecontrol of the decay portion of the percussion intensity envelope thanover the attack portion of the percussion intensity envelope and in theconcept that from a single source of tone signals devoid of vibrato acomposite tone having a percussion envelope combined with a sustainedvibrato phase modulated tone may be produced.

While I have shown and described particular embodiments of my invention,it will be apparent to those skilled in the art that numerousmodifications and variations may be made in the form and constructionthereof, without departing from the more fundamental principles of theinvention. 1 therefore desire, by the following claims, to includewithin the scope of my invention all such similar and modified forms ofthe apparatus disclosed, by which substantially the results of theinvention may be obtained by substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument having a generator of electricalmusical tone signals which are substantially devoid of frequency andamplitude variations, a playing key, a first output channel including anamplifier having means to vary its gain, means to couple the generatorto the first output channel, a switch operable by the playing key tocause the amplifier gain varying means to change the amplifier gain fromsubstantially maximum to minimum value gradually, thereby to cause thetone signals to be transmitted by the amplifier with a percussive decayintensity envelope, a second output channel including phase shift meansfor introducing a vibrato effect into the signals transmitted thereby,means operable by the playing key to cause the generator to transmit asignal to the second output channel, and electroacoustic translatingmeans coupled to the outputs of the channels.

2. In an electrical musical instrument having a plurality of relativelylow impedance electrical tone signal generators, a plurality of signalcollecting bus bars; a manual comprising a plurality of playing keys; aplurality of switches operable by each of said keys, circuits eachincluding said switches and a high impedance element for connectinggenerators ofharmonically related pitches respectively to the signalcollecting bus bars; an amplitude regulating means connected to each ofthe bus bars for determining the relative intensities of the partials ofthe tones to be produced; means for disconnecting one of the amplituderegulating means from its associated bus bar; a first amplifying meansfor amplifying the signals collected by said bus bar; means fortransmitting a portion of the amplified signals to said bus bar; asecond amplifying means for further amplifying another portion of theamplified signal, said last named means including a terminal thepotential of which determines the gain of the last amplifying means;means normally maintaining on said terminal a potential of such value asto cause the last named amplifying means to have maximum gain; meansoperated under the control of one of the playing key operated switchesassociated with each key to cause a gradual change in the poten tial onsaid terminal to a value such as to cause the gain of the last namedamplifying means to be reduced to a minimum; a third amplifying meanscoupled to the signal collecting bus bar; and output means includingelectroacoustic translating means coupled to the outputs of the secondand third amplifiers.

3. For use in a polyphonic electrical musical instrument having playingkeys for the production of individual musical tones and chords having apercussive tone intensity envelope, the combination of an amplifierhaving a terminal the potential of which determines the gain of theamplifier, means normally operating to maintain the potential on saidterminal at such value that it causes the gain to be high, this lastnamed means including a resistance capacitance network, means operableby depression of a playing key to cause the potential on said terminalto change gradually to a value such as will cause minimum gain, the rateof change of the potential on said terminal being determined by saidresistance capacitance network, said last named means operating uponrelease of the key rapidly to change the potential on said terminal to avalue causing high gain.

4. In a polyphonic electrical musical instrument the combination of anelectrical generator of sustained musical tone signals devoid ofvibrato, a switch having a first terminal, a second terminal and aplaying key for operating the switch, a coupling between the firstterminal of said switch and said generator, at first output systemincluding a variable gain means for causing the tones transmittedthereby to have a percussive decay envelope, coupling means between saidfirst output system and the second terminal of said switch, a secondoutput system including means for imparting a vibrato effect into thesignal transmitted thereby, a coupling means connecting said secondoutput system to the second terminal of said switch, and electroacoustictranslating means coupled to the outputs of both of said output systems,whereby closure of said switch produces a percussive vibrator chorustone comprising a steady vibrato component and a gradually decayingnon-vibrato component.

5. In an apparatus for introducing a percussive decay in a musical tonesignal which comprises an electrical musical tone signal source, anoutput system including a signal transmission channel having anamplifier which is provided with a terminal the potential of whichdetermines the amplitude of the ouput signal, means operative when nosignal is supplied by the source to impress a potential of such valueupon said terminal as to cause the amplifier to transmit the signal withhigh gain, and means responsive to the initiation of the transmission ofa tone signal from said source through the signal transmission channelto cause the potential on said terminal to change gradually to a valuesuch as to reduce the gain of the amplifier substantially to zero,whereby the generated tone signal is transmitted with a subsequentpercussive decay.

6. In an electrical musical instrument having a plurality of electricaltone signal generators, playing key operated switches, a plurality ofsignal collectors, a playing key operated means for coupling saidgenerators except one to said signal collectors, an impedance common toall of the signal collectors and connected thereto, an amplifier, meansoperated by the playing key to couple the said one of the generators tosaid amplifier,

signal decoupling means connecting the output of the amplifier to thecommon impedance, a percussion intensity envelope controlling means alsocoupled to the output of said amplifier, and means for amplifying andtranslating into sound the signals which are impressed upon said commonimpedance and the signals produced at the output of the percussionintensity envelope controlling means.

7. In an electrical musical instrument, the combination of a generatorof electrical tone signals, signal amplitude controlling apparatushaving a terminal the potential of which determines the gain thereof, anoutput system including elcctro-acoustic translating means, a playingkey having a first operated means to cause a change in potential on saidterminal to produce a gradual reduction in gain thereof, and a secondplaying key operated means for causing the generator to transmit asignal to the output system after the first means is operated upondepression of the playing key, said first and second means operating inreverse sequence upon release of the key, whereby release of the key iseifective to cause cessation of the generated signal to the outputsystem before permitting the gain of the amplitude controlling apparatusto rise.

8. For use with an electric organ of the type whereinconstant-amplitude, audio-frequency signals are produced in selectedharmonic combinations by depressing one or more manually-operable keys,and wherein said audiofrequency tone signals are to be converted toaudible sound signals for listening pleasure, apparatus for transformingsaid constant-amplitude signals to variable amplitude signals simulatingthe tonal eflect of percussive instruments, comprising, in combination,an input circuit adapted to be coupled to the tone-generating portion ofsaid musical instrument to receive a constantamplitude audio-frequencysignal therefrom, circuit means comprising a sound channel and a controlchannel coupled to said input circuit, alternating-current rectifyingmeans forming part of said control channel and adapted to produce apulse of direct-current voltage substantially simultaneously with thereceipt of a tone signal in said input circuit, resistance-capacitancedischarge means for producing an exponentially-varying control signalupon initiation of a tone signal in said musical instrument, electronicswitch means coupled to said rectifying means and arranged to activatesaid discharge means in response to said direct-current voltage pulse,signal-varying means forming part of said sound channel and coupled tosaid input circuit, said signal-varying means being under the control ofsaid discharge means and arranged to alter the amplitude of the signalfed to said signal-varying means in accordance with the changingmagnitude of said control signal, the variation in magnitude of saidcontrol signal being such as to cause the amplitude of said tone signalto decay rapidly in simulation of the desired percussive tonal eflect,and an output circuit for coupling said decaying tone signal to thesound producing device of said musical instrument.

References Cited in the file of this patent UNITED STATES PATENTS2,216,513 Hammond Oct. 1, 1940 2,276,389 Hammond Mar. 17, 1942 2,310,429Hanert Feb. 9, 1943 2,382,413 Hanert Aug. 14, 1945 2,501,172 Hammond eta1 Mar. 21, 1950 2,563,477 Martin Aug. 7, 1951 2,577,753 Hanert Dec. 11,1951 2,583,566 Hanert Jan. 29, 1952

